The specific aim of this project is to test the effects of a systematic and hierarchical Categorization Program (CP) in patients with moderate to severe traumatic brain injury (TBI) who are enrolled in post-acute rehabilitation. Moderate- severe TBI often results in significant cognitive deficits that hamper the patient's ability to return to pre-injury vocational, educational, and social activities. Consequently, post-acute rehabilitation following TBI often incorporates cognitive retraining. One of the most fundamental cognitive processes is categorization. The ability to divide the world into discrete categories is a rudimentary process beginning early in life and continues to be developed and refined across the lifespan. This underlying process is crucial to a variety of cognitive processes including attention and memory and can influence vocational and educational reintegration. It is hypothesized that the categorization program implemented in this project will be an effective treatment approach to improve categorization abilities following moderate to severe TBI. [unreadable] [unreadable] Researchers and clinicians in the TBI rehabilitation community agree that further research is needed on the effects of cognitive rehabilitation following TBI. Consistent with the 1998 NIH Consensus recommendations, this project implements an innovative treatment program based on a current theoretical model in order to improve cognitive abilities in patients with TBI. The CP is designed to reduce categorization impairment and improve mental flexibility and concept formation, often impaired following moderate-severe traumatic brain injury. The following activities will take place: First, this project will test the effects of a systematic and hierarchical categorization program (CP) in patients with moderate to severe TBI who are enrolled in post-acute rehabilitation. The performance of these subjects will be compared to the performance of subjects who are enrolled in post acute rehabilitation but do not receive the CP. Second, this project will identify the relationship between the categorization tasks, neuropsychologicai performance, functional outcome measures, and patient characteristics such as injury seventy indices. Finally, this project will refine and amend components of the CP in order to further develop the treatment protocol. The long-term objective of this research is to develop effective approaches to remediate complex cognitive processes such as categorization, decision-making and problem solving in patients with moderate to severe (TBI). [unreadable] [unreadable]